Highly Dispersed Metal Nanoparticles in Porous Anodic Alumina Films Prepared by a Breathing Process of Polyacrylamide Hydrogel

The preparation and characterization of highly dispersed metal nanoparticles in porous anodic aluminum oxide (AAO) films are reported. Cross-linked polyacrylamide (PAM) hydrogel nanowires are prepared within the pores of an AAO template by electropolymerization of acrylamide. Metal nanoparticles are introduced into the polymer nanowires in the channels of AAO by a "breathing" mechanism whereby the shrunken polymer nanowires are allowed to swell in an aqueous solution containing metal nanoparticles, and the structures are then re-shrunk in acetone. The loading amount and distribution of nanoparticles in PAM nanowires can be controlled by varying the number of breathing cycles and modifying the breathing process as clearly seen in TEM images. Upon calcination, the nanoparticle/hydrogel composite results in highly dispersed metal nanoparticles supported in AAO. Au nanoparticles (∼12 nm diam.) and Pt nanoparticles (∼3 nm diam.) have been dispersed in PAM nanowires and the channels of AAO films and characterized by TEM, ED, SEM, and X-ray energy dispersion analysis. The assembly strategy will be useful in loading and dispersing of various nanoparticles into the channels of porous materials, as well as into the polymer nanowires.